Last week's cloudy, cool weather brought numerous reports of blue-winged olive hatches, but in some locales the trout weren't necessarily rising to take the newly hatched adult mayflies.

Surprisingly, this isn't that unusual early on in the season, but that doesn't mean you can't have a great day of fishing. You just have to accept the idea that something other than dry fly-fishing may be required. I know this seems like a cruel joke to anglers anxious for surface activity, but let me explain.

I've noticed that the blue-winged olive nymphs are often active for several weeks before significant numbers of adult blue-winged olives appear on the water's surface. In the early season, the trout concentrate their feeding on these active nymphs while mostly ignoring any newly hatched adults (also known as duns).

After those initial weeks of predominantly subsurface feeding, the trout seem to turn on to the increasingly numerous duns on the water's surface and begin rising in earnest to take them.

You can see this for yourself when you're fishing the low, clear water of one of Colorado's Front Range tailwaters. Let's say you get to the river and nothing much is going on, but you do observe a few trout feeding below the surface. That's not unusual, but then you notice that the subsurface feeding activity is steadily increasing, and before long there's a dozen trout in that feeding lane flashing and slashing as they chase down whatever it is they're feeding on beneath the surface.

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As you continue observing this feeding activity, you begin to notice a few freshly hatched blue-winged olive adults on the surface, but the trout ignore them. As time progresses and more adult mayflies appear on the water's surface, a few trout may rise to take them, but the surface feeding remains sporadic at best. Eventually, all feeding activity ends. And you're left wondering why more trout didn't rise.

Ed Engle

What you've just experienced is a typical early-season blue-winged olive hatch where most of the feeding occurs below the surface to the active nymphs. I don't know why the trout don't take more adults from the surface, but I do know I spent a lot of time over the years trying to coax them to take a dry fly when I should have just fished a nymph imitation. Now on days when I see the trout ignoring newly hatched adult blue-winged olives, I switch out my dry fly for the always-dependable pheasant tail nymph or a Barr's blue-winged olive emerger.

An English river keeper named Frank Sawyer invented the pheasant tail nymph more than 60 years ago, and it's still an incredibly effective nymph imitation, especially during the blue-winged olive hatch. He used very fine copper wire in place of thread to bind fibers from a pheasant tail to the hook. The wire gave the fly enough weight to sink in the slow-moving spring creek waters where Sawyer most often fished and added a little flash to the imitation. When Sawyer fished the pheasant tail, he allowed it to swing up in front of the trout to imitate an actively emerging blue-winged olive nymph.

Today most fly-tiers use thread rather than wire to tie the pheasant tail nymph. Weighted versions of the pattern use a brass or tungsten bead. There are dozens of pheasant tail nymph variations nowadays. Some employ synthetics such as Mylar that make a flashier fly, but the sleek silhouette of the fly and the use of natural pheasant tail as the main material still form the basis for the fly's continuing effectiveness.

The Barr emerger, designed by Boulder resident John Barr, combines natural and synthetic materials that effectively imitate the blue-winged olive nymph as it actively emerges toward the water's surface. The fly has stood the test of time since Barr created it in 1975. It should be in every angler's fly box for the springtime "olive" hatch.

I like nymphing the pheasant tail or Barr emerger on a short line. If I can see a trout feeding under the water's surface, I simply watch for it to take the fly. If the trout isn't visible, I work to keep as much slack out of the leader as possible as the fly drifts naturally downstream. The "tight line" keeps me in contact with the fly and makes it easier to detect strikes.

I prefer unweighted blue-winged olive nymph imitations because I think unweighted nymphs are more active in the water column, which imitates the living insect more closely. I attach a split shot to the leader or use a weighted fly as part of a two-fly-nymphing rig to get the unweighted nymph down. You should start by dead drifting the nymph imitation, but if that doesn't elicit a strike, try "activating" the nymph by lifting or slowly swinging it to the water's surface to imitate the active swimming of the naturals.

Of course, it's only a matter of time before the trout do start taking the newly hatched blue-winged olive adults from the water's surface, and your attention will gravitate toward fishing dry fly imitations. But even then, you may want to trail a trusty pheasant tail nymph or blue-winged olive Barr emerger behind your dry fly imitation just in case there are trout that are still in the mood for a nymph.

As always, the key is to observe the trout's feeding behavior and go from there. It's as simple as doing what the trout tell you to do ... .

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